Add shared Copilot CLI marketplace manifest and plugin layout

[fahreddinozcan]

Summary

• add a Copilot CLI marketplace manifest under .github/plugin/marketplace.json
• move Claude and Copilot plugin payload files into a shared plugins/context7 source
• keep separate Copilot and Claude manifests in the shared plugin root
• add Copilot CLI docs and update client docs links

Validation

• claude plugin validate ./plugins/context7
• claude plugin marketplace add ./ --scope local
• claude plugin install context7-plugin@context7-marketplace --scope local
• copilot plugin marketplace add .
• copilot plugin install context7-plugin@context7-marketplace
• copilot plugin marketplace browse context7-marketplace
• copilot plugin list

[linear]

CTX7-1509 Update Copilot CLI Plugin Marketplace Manifest

[mintlify]

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Project	Status	Preview	Updated (UTC)
context7	🟢 Ready	View Preview	Apr 7, 2026, 4:18 PM